Aircraft have seen enormous advances in technology over the last century. For example, in just the recent past, aircraft engines, pumps, and other actuators have become quieter, autopilots have become smoother, and automation has taken a greater role in aircraft control. But, these technological advances have also resulted in pilots becoming increasingly removed from the direct control of the aircraft. Further, these advances have resulted in pilots having less direct feedback about the operation of the aircraft systems and flight control actions.
An example of less feedback is the throttle lever on the Airbus A320 aircraft, which remains in a fixed position while the autothrottle system is issuing throttle commands to the engines. Thus, the only indication the pilots have of the actions of the autothrottle system is the movement of the N1 engine indicator, which shows the turbine engine rotation speed.
Further, noise from air flow over the cockpit prevents the crew from hearing the engines, and the autopilot and autothrottle systems are smooth enough, so that it is often difficult for the pilot to detect aircraft maneuvers.
Without a system that gives better feedback to the pilots, all of the above factors can combine to cause pilots to lose track of the operation of the aircraft's automated systems with potentially disastrous results.